A centrifugal compressor includes one or more impellers that compress a fluid. The impellers are mounted on a rotating shaft which is supported by a plurality of bearings. The bearings require a steady supply of lubricant, which is oftentimes oil. However, in some recent applications, refrigerant has been used to lubricate the bearings rather than oil. Refrigerant lubrication can be used when, for example, the compressor is part of a refrigeration chiller. A refrigeration chiller removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. The cooled liquid may then be used to cool air (e.g., air conditioning) or in an industrial process.
A pump can be used to make the refrigerant to flow to the bearings. The pump may cavitate making it more difficult to supply the refrigerant to the bearings. There can also be operating conditions under which the supply of refrigerant is in inadequate supply or the state of the refrigerant is a mix of liquid and vapor such that it is unable to properly lubricate the bearings. Therefore, what is needed is a backup lubricant supply system that is capable of providing lubricant (e.g., refrigerant) to the bearings when the primary lubricant supply system is unable to lubricate the bearings.